This invention relates to orthopedic casts and casting methods especially suited for, but not limited to, intermediate phase or orthopedic rehabilitation.
Orthopedic rehabilitation typically occurs in three successive phases: the acute phase immediately following injury or surgery; the intermediate phase during which function is improving; and the chronic phase when function has reached a plateau. The intermediate phase is a variable period extending from approximately 6-8 weeks to approximately 6-8 months after trauma or surgery. The patient population within this phase generally includes those who have achieved preliminary tissue healing, but for whom continued rehabilitation can improve function, and who require removable external fixation devices for mechanical support, prevention of deformity, or maintenance of corrected posture for a limited period.
Plaster casts provide the accepted mode of fixation during the acute phase, whereas orthotic devices are customarily employed during the chronic phase. During the intermediate phase, however, neither plaster nor orthotic devices offer the most effective and economical fixation. Plaster is brittle, possesses low impact and fatigue resistance, cannot be reformed once set, is susceptable to deterioration or damage when exposed to water or urine, and is of excessive weight. In many practical intermediate phase applications, therefore, plaster requires frequent cast replacement, the use of abduction bars, struts and/or heavy reinforcement to prevent cracking, and often results in substantial inconvenience and expense to the patient.
One intermediate phase application which demonstrates some of the drawbacks of plaster is the so-called "bivalve". A bivalve is a removable cast which is formed of two discrete sections adapted to be secured together about the limb or body to provide appropriate fixation. The weight of a plaster bivalve tends to be intolerable, especially to a patient already handicapped by muscle weakness, and may mean the difference between walking and sitting, between patient acceptance and rejection. Furthermore, unlike trauma casts, plaster bivalves require additional labor for lining, padding, petaling, and fitting. These labor costs are multiplied during prolonged use by soiling, breakage, and serial corrections. Curing time adds hidden costs incident to extra hospital days or return visits and so, when examined in this context, plaster bivalves tend to be uneconomical.
Orthotic devices are easily removable and provide variable rigidity and high fatigue resistance, all necessary in the construction of removable intermediate phase rehabilitative devices. Orthotic devices achieve this by using metal for rigidity and leather for flexible cuffs, in combination with sheet plastics. Their structural properties therefore are appropriate for intermediate phase usage; but fabrication requirements are too expensive for the limited use most commonly associated with such usage. More specially, orthotic devices, when fabricated from sheet plastic, require the experience of a trained orthotist, extensive vacuum forming equipment, and frequently a week or more of fabrication time. Modification of such a device during periods of improving function is likewise difficult.
Synthetic casting materials may be utilized to provide lightweight, durable casts in a wide variety of shapes; however, until this invention, synthetic casting materials have been viewed and marketed most commonly as plaster substitutes. As a consequence, splints, rolls, lining, and padding for usage with these casting materials have been designed to appear and function as equivalents to plaster cast components, and these materials have been correspondingly applied like plaster, to make plaster-like casts, primarily during the acute phase.
One thermoplastic material which is suited for usage as an orthopedic casting material is epsilon polycapriolactone; however, this material heretofore has been applied predominately as a plaster substitute in the fabrication of small trauma casts for acute phase application. A woven cotten mesh coated with this material is commercially available in rolls and splints from Hexcel Corporation, Dublin, California as "Hexcelite". At room temperature, epsilon polycapriolactone has a crystalline molecular structure and its surface texture is stiff and hard. When heated in a water bath to about 80.degree. C. (170.degree. F.), it becomes amorphous, plastic, and self-adhesive. Upon cooling, it returns to its original state. This is a repeatable cycle of physical change, without chemical reaction. The aforementioned casting material typically is utilized with a polypropylene stockinette. This type of stockinette, however, tends to be unsatisfactory because it can be allergenic, wets immediately, retains large amounts of water, and dries slowly. When wet, it has a clamy, distinctly unpleasant feeling next to the skin. Additionally, the aforementioned casting material commonly is utilized with different types of padding materials, such as green foam rolls, or "Reston" foam sheets, which are disposed between it and the stockinette. Neither of these padding materials is completely satisfactory. The green foam rolls are composed of 1/16th inch thick open cell polypropylene foam which is thin and very compressible. Although perhaps adequate for simple casts, even in multiple layers, it does not provide good protection under localizers or walking casts, where there is heavy cast pressure. Furthermore, the foam is not self-adherent and multiple layers often are needed for padding. When a cast is bivalved, therefore, these layers come apart and recoil into lumps under the lining. "Reston" foam sheets are composed of a 1/2 inch thick open cell sheet foam, which has good padding properties and is representative of a wide variety of open cell medical foam products available for padding. Open cell foam construction, however, has significant disadvantages in long term cast use in that the open cells break down under prolonged shear forces, and tend to retain water, urine, stool and skin debris.